icuSources/common/umutex.h

   1 /*
   2 **********************************************************************
   3 *   Copyright (C) 1997-2005, International Business Machines
   4 *   Corporation and others.  All Rights Reserved.
   5 **********************************************************************
   6 *
   7 * File UMUTEX.H
   8 *
   9 * Modification History:
  10 *
  11 *   Date        Name        Description
  12 *   04/02/97  aliu        Creation.
  13 *   04/07/99  srl         rewrite - C interface, multiple mutices
  14 *   05/13/99  stephen     Changed to umutex (from cmutex)
  15 ******************************************************************************
  16 */
  17
  18 #ifndef UMUTEX_H
  19 #define UMUTEX_H
  20
  21 #include "unicode/utypes.h"
  22 #include "unicode/uclean.h"
  23
  24
  25 /* APP_NO_THREADS is an old symbol. We'll honour it if present. */
  26 #ifdef APP_NO_THREADS
  27 # define ICU_USE_THREADS 0
  28 #endif
  29
  30 /* ICU_USE_THREADS
  31  *
  32  *   Allows thread support (use of mutexes) to be compiled out of ICU.
  33  *   Default: use threads.
  34  *   Even with thread support compiled out, applications may override the
  35  *   (empty) mutex implementation with the u_setMutexFunctions() functions.
  36  */
  37 #ifndef ICU_USE_THREADS
  38 # define ICU_USE_THREADS 1
  39 #endif
  40
  41 /**
  42  * By default assume that we are on a machine with a weak memory model,
  43  * and the double check lock won't work reliably.
  44  */
  45 #if !defined(UMTX_STRONG_MEMORY_MODEL)
  46 #define UMTX_STRONG_MEMORY_MODEL 0
  47 #endif
  48
  49 /**
  50  * \def UMTX_CHECK
  51  * Encapsulates a safe check for an expression (usually a condition)
  52  * for lazy variable inititialization.
  53  * On CPUs with weak memory models, this must use memory fence instructions
  54  * or mutexes.
  55  * @internal
  56  */
  57 #if UMTX_STRONG_MEMORY_MODEL
  58
  59 #define UMTX_CHECK(pMutex, expression, result) \
  60     (result)=(expression);
  61
  62 #else
  63
  64 #define UMTX_CHECK(pMutex, expression, result) \
  65     umtx_lock(pMutex); \
  66     (result)=(expression); \
  67     umtx_unlock(pMutex);
  68
  69 #endif
  70
  71 /*
  72  * Code within ICU that accesses shared static or global data should
  73  * instantiate a Mutex object while doing so.  The unnamed global mutex
  74  * is used throughout ICU, so keep locking short and sweet.
  75  *
  76  * For example:
  77  *
  78  * void Function(int arg1, int arg2)
  79  * {
  80  *   static Object* foo;     // Shared read-write object
  81  *   umtx_lock(NULL);        // Lock the ICU global mutex
  82  *   foo->Method();
  83  *   umtx_unlock(NULL);
  84  * }
  85  *
  86  * an alternative C++ mutex API is defined in the file common/mutex.h
  87  */
  88
  89 /* Lock a mutex.
  90  * @param mutex The given mutex to be locked.  Pass NULL to specify
  91  *              the global ICU mutex.  Recursive locks are an error
  92  *              and may cause a deadlock on some platforms.
  93  */
  94 U_CAPI void U_EXPORT2 umtx_lock   ( UMTX* mutex );
  95
  96 /* Unlock a mutex. Pass in NULL if you want the single global
  97    mutex.
  98  * @param mutex The given mutex to be unlocked.  Pass NULL to specify
  99  *              the global ICU mutex.
 100  */
 101 U_CAPI void U_EXPORT2 umtx_unlock ( UMTX* mutex );
 102
 103 /* Initialize a mutex. Use it this way:
 104    umtx_init( &aMutex );
 105  * ICU Mutexes do not need explicit initialization before use.  Use of this
 106  *   function is not necessary.
 107  * Initialization of an already initialized mutex has no effect, and is safe to do.
 108  * Initialization of mutexes is thread safe.  Two threads can concurrently
 109  *   initialize the same mutex without causing problems.
 110  * @param mutex The given mutex to be initialized
 111  */
 112 U_CAPI void U_EXPORT2 umtx_init   ( UMTX* mutex );
 113
 114 /* Destroy a mutex. This will free the resources of a mutex.
 115  * Use it this way:
 116  *   umtx_destroy( &aMutex );
 117  * Destroying an already destroyed mutex has no effect, and causes no problems.
 118  * This function is not thread safe.  Two threads must not attempt to concurrently
 119  *   destroy the same mutex.
 120  * @param mutex The given mutex to be destroyed.
 121  */
 122 U_CAPI void U_EXPORT2 umtx_destroy( UMTX *mutex );
 123
 124
 125
 126 /*
 127  * Atomic Increment and Decrement of an int32_t value.
 128  *
 129  * Return Values:
 130  *   If the result of the operation is zero, the return zero.
 131  *   If the result of the operation is not zero, the sign of returned value
 132  *      is the same as the sign of the result, but the returned value itself may
 133  *      be different from the result of the operation.
 134  */
 135 U_CAPI int32_t U_EXPORT2 umtx_atomic_inc(int32_t *);
 136 U_CAPI int32_t U_EXPORT2 umtx_atomic_dec(int32_t *);
 137
 138
 139 #endif /*_CMUTEX*/
 140 /*eof*/
 141
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 143